Susceptors are understood to be components which are located in the immediate region of the process and either serve for receiving the articles to be treated or surround these in the form of a chamber, so that the process space is largely partitioned off.
The susceptors rest on a carrying structure which is likewise composed of graphite or CFC (CFC: Carbon Fiber Composites). CFC materials are carbon fiber composite materials for high-temperature applications, for example in a furnace. The susceptors are closed at both ends by means of a graphite cover, which graphite covers are mostly suspended on the furnace doors and can therefore be opened and closed in a simple way.
For high-temperature processes, heating elements, mostly bar-type heating elements, are arranged around the susceptor in uniform intervals.
An example of a profiled susceptor for reception of semiconductor wafers in a thermomigration plant may be gathered from EP 1 590 510 B1.
Susceptors are used in vacuum process plants which serve for the production and processing of components made from engineering ceramics, hard metal and other alloys, the components being acted upon by a gas pressure and high temperatures. In particular, the susceptors serve for delimiting the process space with respect to the insulation or other furnace components, so that these are protected from an excessive temperature load or load caused by aggressive gases.
A fundamental problem is the thermal expansion of the susceptor in the course of the process. Depending on the position and size of the useful space, a susceptor can no longer be manufactured from a graphite block. Particularly when the susceptor, as seen in cross section, corresponds to a flattened tube or is of tunnel-like design, this causes the problem that, where appropriate, different crude blocks or even different raw materials have to be used for manufacturing the components.
This has the negative result that the individual components of the susceptor have differences in terms of thermal expansion. The result of this, in turn, is that the durability of the components is restricted, and that the susceptor becomes leaky in relation to the remaining furnace space. The performance of the process plants is thereby impaired, and process parameter flexibility is greatly restricted.
Another problem arises from the use of whole crude blocks for flattened tubes (susceptors) because of the considerable consumption of material, since large cores occur. Since large crude blocks mostly are not compacted so well in the core, the cut-out cores or the residual material cannot be used unrestrictedly for other applications.